Yanmar 3JH40 Water Pump Impeller Replacement
A worn impeller on your Yanmar 3JH40 starves the engine of cooling water and can overheat it in minutes. Below is the exact water-pump kit that fits this engine, a step-by-step video, and the parts you need to do the job yourself.
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Watch: how to replace it (step by step)
How to Replace Impeller – Yanmar 3H M35F
yanmar impeller change part 3
Tools Needed
- Hammer
- Screwdriver
Safety
- Be careful when using the hammer to avoid damaging surrounding areas.
- Ensure the area is well-ventilated when applying gasket maker.
Steps
- Remove the bottom bolts of the housing to separate it.
- Use a hammer to carefully tap the housing until it comes off.
- Be cautious while removing the housing, especially if there is teak nearby.
- Locate the housing for the water pump.
- Remove the cover of the water pump by unscrewing the four screws.
Tips
- If the housing is stuck, use a hammer to gently tap it until it comes off.
- Apply gray gasket maker around the housing to reseal it after reinstallation.
Which part do I need for my Yanmar 3JH40?
For most 3JH40 owners the part above (YAN129670-42610) is the right choice.
Frequently asked questions
What water pump impeller fits a Yanmar 3JH40?
The Yanmar 3JH40 uses the impeller sold as YAN129670-42610. Confirm the number against your engine's model code and year plate before ordering.
How often should I replace the impeller on a Yanmar 3JH40?
Replace the water pump impeller every 1-3 years or roughly every 200-300 running hours, whichever comes first — and sooner if you run in silty, sandy or shallow water.
What are the symptoms of a failing impeller on a Yanmar 3JH40?
A weak or missing telltale stream, engine temperature climbing above normal, or an overheat alarm are the classic warning signs. A worn impeller can overheat and damage the engine within minutes, so don't delay the job.
Do I need the full water pump kit or just the impeller?
For the 3JH40, fit the complete kit. The seals, O-rings, gasket and wear plate age alongside the impeller, and replacing them together is the reliable, do-it-once job.
How long does a water pump job take on a Yanmar 3JH40?
For a competent DIYer it's typically a 1-2 hour job of medium difficulty. The video above shows the job on a similar Yanmar diesel engine — the procedure matches, but check the 3JH40 manual for model-specific details.
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